Abstract
The initial dissolution rate measurement method was applied to physical forms of sulfanilamide, two polymorphs and a hydrate. As the result, the transition temperatures and the heats of transition between the metastable α-and the stable β-forms, and between the β-and the hydrated forms were determined to be -119°, 0.17 kcal/mole, and 38.3°, 1.74 kcal/mole, respectively. At the same time, thermal behaviors and solubilities of all the known forms of sulfanilamide including the above three were investigated by other methods such as differential scanning calorimetry and conventional solubility measurement. Data obtained agree well with those by dissolution study, though direct solubility determination of the metastable α-form was impossible because of rapid conversion to the β-or to the hydrated form. Thus, the total relation among these physical forms could be more clearly understood by combining all these data, and the supposition proposed previously that the α-form was monotropic with respect to the β-polymorph was denied completely.
